While breastfeeding is clearly associated with lower rates of infant morbidity particularly among disadvantaged populations, no carefully controlled study has demonstrated that infant morbidity can be reduced through the promotion of breastfeeding. The Navajo Infant Feeding and Morbidity Project is designed to demonstrate that increases in rates of exclusive breastfeeding are associated with declines in morbidity due to respiratory and gastrointestinal illness among Navajo infants. A rigorous test of this relationship will be possible because of unique features of the research site, including a completed breastfeeding promotion project which has substantially increased breastfeeding rates, high infant morbidity combined with lack of financial barriers to health care, and access to the medical records for all infants born in the study area. Aims of the project are to: 1) assess the effect of the breastfeeding promotion on breastfeeding rates, 2) assess rates of common childhood illnesses prior to and after promoting breast feeding, 3) relate infant morbidity to changing feeding patterns, and 4) document subsequent changes in health care costs. The project will use medical records to evaluate longitudinal changes in infant feeding practices and illness rates before and after the breast feeding promotion program in Shiprock, NM. The medical records will be obtained for all infants born in the year before and the year after the promotion, roughly 2000 infants. Data will be collected regarding initiation and duration of breast feeding, and illness episodes such as respiratory and gastrointestinal illness, otitis media, bacteremia, meningitis, and eczema. Hospital costs to administer formula, including staff time caring infants in the nursery, and money saved through declines in illness visits and hospitalizations, will be assessed along with community expenses for formula. We anticipate that while the proportion of infants experiencing illness in each feeding group will remain constant over time, community rates of illness will decline as the intervention affects the proportion of infants breastfed. If breastfeeding is shown to decrease infant morbidity, the project will have identified a low cost intervention which improves the health of infants, cuts health care costs, and is particularly applicable to disadvantaged populations.